The present invention relates to an intravascular catheter. In particular, the present invention relates to an intravascular catheter, such as a dilatation balloon catheter, of the type which is advanced over a guide wire having a distal guide wire lumen which is shorter than the length of the catheter and which extends through the balloon of the catheter.
Angioplasty procedures have gained wide acceptance in recent years as efficient and effective methods for treating types of vascular disease. In particular, angioplasty is widely used for opening stenoses in the coronary arteries, although it is also used for the treatment of stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Typically, in coronary procedures a hollow guide catheter is used in guiding the dilatation catheter through the vascular system to a position near the stenosis (e.g., to the coronary artery ostia). Using fluoroscopy, the physician guides the dilatation catheter the remaining distance through the vascular system until a balloon is positioned to cross the stenosis. The balloon is then inflated by supplying fluid under pressure, through an inflation lumen in the catheter, to the balloon. The inflation of the balloon causes a widening of the lumen of the artery to reestablish acceptable blood flow through the artery. In procedures in the peripheral vessels (vessels other than coronary vessels) the guide catheter may not always be used.
Preferably a catheter will have several physical characteristics. First, there has been a continuing effort to reduce the profile and shaft size of the dilatation catheter so that the catheter not only can reach but also can cross a very tight stenosis. Portions of dilatation catheter must also be sufficiently flexible to pass through tight curvatures especially in the coronary arteries. The ability of a catheter to bend and advance through the vasculature is commonly referenced to as the "trackability of the catheter." A further requirement of a dilatation catheter is its "pushability." This involves the transmission of longitudinal forces along the catheter from its proximal end to its distal end so that a physician can push the catheter through the vascular system and the stenoses. The catheter should be both relatively trackable and pushable.
Two commonly used types of dilatation catheters are referred to as "over-the-wire" catheters and "non-over-the-wire" catheters. An over-the-wire catheter is one in which a separate guide wire lumen is provided in the catheter so that a guide wire can be used to establish the path through the stenoses. The dilatation catheter can then be advanced over the guide wire until the balloon on the catheter is positioned within the stenosis.
In some over-the-wire catheters, the guide wire lumen does not extend the entire length of the catheter. In this type of catheter, the guide wire lumen extends only from the distal end of the balloon to a point proximal of the balloon but distal of the proximal end of the catheter.
It is sometimes desirable to use a smaller or larger balloon than that initially used. The catheter is preferably exchanged by leaving the guide wire in place and using it as a guide for the next catheter. It is said that shortened guide wire lumen type catheters are easier to exchange than catheters having the guide wire lumen extending the entire length of the catheter.
While several structures for shortened guide wire lumen dilatation catheters have been proposed, these structures suffer from several disadvantages. For example, some catheters have relatively flexible one-piece plastic design. Because the distal end of the guide wire exits the catheter near the distal end of the shaft portion, the guide wire cannot contribute to the pushability of the majority of the shaft portion. Thus, the proximal shaft portion of such catheters has low column strength. With such a configuration, the catheter shaft and the portion of the guide wire which extends outside of the guide wire lumen will tend to separate toward opposite walls of the artery as the catheter is advanced or retracted. That is, the shafts and guide wire tend to "scissor" and bow, buckle and the shaft may even kink when the balloon is advanced or retracted across a lesion. This scissoring or bowing may lead to abrasions to the inner lining of the artery. This scissoring or bowing also leads to poor pushability and trackability of the catheter. To counteract this deficiency, some known designs have extended the length of the guide wire lumen and/or provided additional stiffener elements in the shaft.
In one recently developed design, a large part of the proximal catheter shaft is made of a metallic tube (commonly referred to as a hypotube). As described in more detail below, the hypotube construction provides the desired pushability and yet may have a relatively small outer diameter or profile.
In catheters of this hypotube design, the inlet for the guide wire lumen is usually placed near or adjacent to the distal end of the hypotube. (The "inlet" to the guide wire lumen here refers to the proximal guide wire lumen aperture and the "outlet" to the guide wire lumen refers to the distal guide wire lumen aperture.) This location of the guide wire inlet, however, may not always be at a location which is the most desirable. If the guide wire inlet is placed adjacent the distal end of the hypotube, either the flexible plastic shaft segment will be short or the guide wire lumen will be relatively long.
On the other hand, placing the guide wire lumen inlet distally of the distal end of the hypotube (in the plastic shaft segment) has several disadvantages with presently available designs. The hypotube is relatively stiff and the plastic segment is relatively flexible. The part of the plastic shaft segment through which the guide wire runs will also be relatively stiff when the guide wire is in place (compared to the part of the plastic segment through which the guide wire does not run). Thus, if the guide wire inlet is placed distally of the distal end of the hypotube, a relatively flexible section is defined between two relatively stiff sections. Such a configuration will tend to bend or buckle in the relatively flexible area as an attempt is made to advance the catheter through the vasculature. Therefore, the responsiveness of the catheter will be substantially diminished. Further, the catheter might tend to kink at the section between the two relatively stiff sections. Such kinking would tend to close the inflation lumen--an obviously undesirable event.
Therefore, it is an object of the present invention to provide an over-the-wire catheter of the short guide wire lumen type having improved pushability and trackability.